Method for marking sheet metal blanks and for welding can bodies from marked sheet metal blanks

ABSTRACT

A method for marking tin coated sheet metal blanks is provided in which the marking is indicative whether the blank comprises an edge region that includes a tin coating thicker than the rest of the blank. This marking is preferably brought on the blanks when a plurality of blanks is cut from a sheet metal plate. In the alternative the marking may have been applied to the sheet metal plate already. The sheet metal blanks thus marked are provided in form of a stack comprising marked and unmarked blanks, depending on whether there is a thicker edge region coating present on the individual blank or not. When making container bodies of these blanks by de-stacking and rounding the sheet metal blanks and welding the longitudinal seam of the rounded container body blanks, the marking is read in the container making apparatus and at least one welding parameter is changed for welding container body blanks with a marking in comparison with container body blanks without marking.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Swiss patent application No. 00730/08, filed May 14, 2008, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The invention relates to a method for providing coated and in particular tin coated sheet metal blanks for container body making and in particular can body making. The invention further relates to a stack of tin coated sheet metal blanks for container body making. Further the invention relates to a method of making container bodies from such tin coated sheet metal blanks on such a stack. The invention further relates to a double slitter for cutting sheet metal plates to sheet metal blanks and to a container body making apparatus.

PRIOR ART

It is known for making containers and in particular can bodies with a longitudinal weld seam, to cut large plates from a tin coated metal band that is taken from a coil. This step of providing sheet metal plates from the band can follow directly after the production and the coating of the sheet metal band or can follow later. For the making of containers and in particular cans, these plates, having for example a size of 100 by 100 centimeters or a size 60 by 60 centimeters are fed in form of a stack of such plates to a double slitter or angular slitter, respectively. Therein the plates are de-stacked and each plate is cut by two rows of cutters arranged at a right angle to each other. Thus a plate is first cut into metal sheet strips and then the strips are cut to single sheet metal blanks. These sheet metal blanks are collected together and are stacked. In a later stage such stacks are brought into a device that produces welded can body blanks from the sheet metal blanks. To this end single sheet metal blanks are de-stacked from the stack and fed to a rounding apparatus which rounds the sheets to a body blank. This body blank is fed to a welding machine of the device in which the edges of the blank are brought in an overlapping position (or if the case may be in an abutting position) and are then welded. The welding is usually done by electrical welding with welding rollers and in most cases with wire electrodes running on the rollers which provide welding electrodes that are continuously renewed. This is an advantage in view of the tin coated sheet metal.

The sheet metal band that is taken from the coil has a thicker tin coating at the edge regions of the band due to the production process. The sheet metal band may have a desirable coating value of 1.0 grams per square meter in the middle of the band. A narrow region at each edge may at the same time have a tin coating of 4.0 grams per square meter. Depending on the tin coating a different electric welding current is necessary for welding. For example, with a tin coating of 0.8 grams per square inch a welding current of 4000 Ampere may already be too high for a high quality weld seam while a tin coating of 3.0 grams per square meter may necessitate a welding current of 4200 Ampere. The edge regions of the sheet metal band are thus problematic for the welding of container bodies. This is particularly true if the plates are cut from the band in such a way that the edge regions with too much tin coating form the seam of the body blanks (so called H-Grain). With another type of cut (C-Grain) the edge regions of the plate form the upper or lower edge of the body blank so that the excessive tin coating is only detrimental to welding at the beginning or end of the weld seam. But this as well may lead to welding errors since the beginning and the end of welding are critical welding areas anyway.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to overcome these drawbacks.

Now, in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the method for providing sheet metal blanks includes the coating dependent marking of the sheet metal by means of a machine-readable marking to distinguish between regions of greater and lesser thickness. A stack of tin coated sheet metal blanks provided with markings on the blanks with thicker tin coating allows solving the problem during container marking by changing welding parameters during welding in dependency on the marking. The method for making container bodies as claimed can thus avoid the mentioned drawbacks. A double slitter and a container making apparatus are provided by the invention which provides a solution of the mentioned problems.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the dependent claims and to the following detailed description of preferred embodiments. Such description makes reference to the annexed drawings, wherein

FIG. 1 shows a schematic view from above onto a double slitter according to the invention;

FIG. 2 shows a schematic view from above onto a welding apparatus according to the invention;

FIG. 3 shows a schematic side view of the welding apparatus of FIG. 2; and

FIG. 4 shows a schematic representation of a sheet metal coil and the sheet metal band uncoiled from the coil as well as different kinds of cutting of the sheet metal blanks from a sheet metal plate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 4 shows in a schematic representation a coil 37 of a coated sheet metal band 36. In the following description a tin coating is presumed as it is used for making container blanks and in particular can body blanks. The coating may be present on both sides of the band 36 or only on one side. The sheet metal band may have a width of 100 centimeters and a length of 100 meters or more. These dimensions are to be understood as an example only. Instead of the tin coating a different known coating may be present which is as well prone to the problem of not being equally distributed over the width and/or the length of the sheet metal band. With a tin coating the unequal distribution is usually present such that the edge regions 38 and 39 of the band 36 have a considerably thicker tin coating than the region in between. The thickness of the tin coating in the edge regions may be three times greater than on the other parts of the band. The band 36 may have a thickness in the middle of the band that corresponds to a coating of 0.8 grams per square meter while the edge regions with a width of 1.0 centimeter are coated with a coating of 3.0 grams per square meter leading to a corresponding greater thickness of the coating in these edge regions. These differences in the coating are caused by the production of the band and are therefore known to be present in all of such sheet metal bands. According to the first variant I shown in FIG. 4 plates 6 are cut from band 36 (by known cutting machines not shown here). The plates are the stacked and later cut in an angular slitter or double slitter, respectively, first in strips 7, 8 and 9 by first cuts (cut lines a, b) and then by second cuts (cut lines c to f) into (in this example) fifteen sheet metal blanks. The plates 6 have a length TL and a width of the plate WB/TB that equals the width of the band 36. The shown cuts of this variant I are such that the width of each the strips 7, 8 and 9 determines the circumference of the container body 30 that is made by the sheet metal blanks (one of this blanks is referenced by the numeral 18). The height h of the second cuts determines the height of the container body blank 30. It can be seen that with this variant of cutting the plate the edge regions 38 and 39 of strips 7 and 9 form part of the longitudinal seam of a container body 30 that is made by the sheet metal blanks comprising the edge regions (blank 18 being one of these blanks). The higher thickness of the tin coating of these sheet metal blanks necessitates a different setting of the welding current of the welding machine (or of another welding parameter) than for those blanks that have been cut from strip 8 and do not have the thicker coating.

When the sheet metal band 36 is cut as shown as variant II in FIG. 4, then the first cuts (cut lines g, h, i and j) of the double slitter determine the height h of the can body blank 30′ and the second cuts (cut lines 1 and k) determine the circumference of the body blank 30′. In this case the thicker coating is only present at the beginning or the end of the weld seam of the can body blanks made from strips 7 and 9. But this as well may give problems with welding compared to the can bodies made from strips 8, 8′ and 8″ located between strips 7 and 9.

Now, FIG. 1 shows a solution wherein the sheet metal blanks, which have a higher tin coating thickness in their edge region are provided with a marking. FIG. 1 shows in a schematic representation a double slitter 1 which makes the cuts generally as explained before under variant I of FIG. 4. But in this case only nine sheet metal blanks are cut from each plate 6 and not fifteen blanks as in FIG. 4. The double or angular slitter 1 has a stack receiving section for taking up a stack of plates 6. Plate 6 is a tin coated plate as explained above. A single plate 6 is de-stacked and fed through first cutting means 2 (which are known to the skilled person) and which cuts the plate into three strips 7, 8 and 9. Afterwards the strips 7, 8 and 9 are fed to the second cutting means 3 positioned at a right angle to the first cutting means 2. By the second cutter 3 the strips are cut into sheet metal blanks 10 to 18.

In this embodiment of the invention there are provided marking devices 4 and 5 which apply a marking 20 to the edge region 39 of the plate and a marking 21 to the edge region 38 of the plate 6 when the plate is fed to the cutter 2. After cutting these markings 20 and 21 are present on strips 7 and 9, respectively, as shown with lines on these strips. These markings may for example be made by a continuous application of a thin strip of a marking substance and in particular a colour or a lacquer and would then look like lines 20 and 21 in FIG. 1. Instead of a fully continuously marking by a line, a marking can be done as well by a discontinuous application of single points or strips or other symbols provided by the marking substance and in particular colour marking substance. These symbols may follow each other in a predetermined distance. The marking devices 4 and 5 may comprise nozzles or other means that provide for jets of a marking substance directed to the sheet metal plate 6. Such markings may be made on one side of the plate only, so on the upper side of plate 6 as shown in FIG. 1 or on the lower side that can not be seen in FIG. 1, or on both sides of the plate 6. As a result single sheet metal blanks 10 to 18 are provided after the second cut of which blanks 10 to 12 and 16 to 18 having a thicker tin coating are marked with markings 20 and 21. When a stack 22 is formed by such blanks produced from several plates 6, this stack contains sheet metal blanks with markings and sheet metal blanks without markings depending on the presence of a thicker tin coating or not on each blank. The collecting of the sheet metal blanks 10 to 18 at the output of the second cutter 3 and the making of a stack of sheet metal blanks from several plates 6 is known to the skilled person and is not explained here in detail. These known steps do not change with the present invention.

The position of the marking devices 4 and 5 in front of the cutter 2 is only shown as a preferred example. The devices may as well be positioned after the cutter 2 so that the cut strips 7 and 9 move under the devices (or over the devices in case of marking the lower surface additionally or in the alternative). The marking devices can be fixed devices or may as well be movable devices that move over the plate or over the strips. The markings may be applied to only one side of the sheet metal or to both sides of the sheet metal.

The marking can be done as well for sheet metal plates 6 that are cut according to the cuts of variant II of FIG. 4.

Instead of the preferred marking within the slitter 1 the marking can be provided as well during production of the sheet metal band 36, for example during coiling of the band. On the other hand the marking of the edge regions 38 and 39 can be performed during uncoiling of the band 36 and cutting of the plates 6 from the band 36. These plates are then already provided with markings 20, 21 so that such markings have not to be provided in the slitter. The slitter may comprise marking devices 4 and 5 nevertheless, so that both kinds of plates can be used, pre-marked plates and unmarked plates. The steps of producing the sheet metal band and coiling are made at the sheet metal manufacturer's which in this case provides the marking. The steps of uncoiling and cutting plates are done separately, either at the sheet band manufacturer's premises as well, who in this case provides again the marking, or these steps are done by the can-maker providing the marking when doing these steps. The cutting of the plates 6 to blanks 10 to 18 is usually done by the can-maker which then may provide the marking during these steps as explained above.

In a following production step for making cans, can bodies are made from the stacked blanks of stack 22. FIGS. 2 and 3 schematically show a can body making apparatus 35 in view from above and from one side. Single blanks are de-stacked from stack 22 and blank 18 is shown as an example for such a de-stacked sheet metal blank. A transport device not shown but well known to the skilled person conveys blank 18 to a rounding apparatus 24 which rounds the flat blank to a rounded can body blank 28. This body blank 28 is further conveyed by the same or a different transport device, such as a belt drive or a chain drive, to the welding apparatus 25 in which the facing edges of the rounded blank 28 are brought in an overlapping or abutting relation and are welded by welding rollers 23, 23′ and wire electrodes (not shown) to the can body 30. FIG. 3 shows a rounded blank 29 that is already inserted between the welding rollers and is being welded and wherein the lower welding roller 23′, which is in fact hidden by the blank, is shown nevertheless. In FIG. 2 it is shown that blank 18 is provided with the machine-detectable marking 21 which can be detected by a detector 26. The detector may be an optical detector detecting the visible marking 21 or an invisible marking (to the human eye) which is detectable by the detector. Such detectors are well known in the art from other technical uses and are not explained here in detail. If the marking is for example a magnetic lacquer, the detector is of course selected such that it is able to detect this kind of marking. The detector 26 sends the detection signal 31 preferably directly to the control device 27 of the welding apparatus 25 (or to a main controller of the production line that is connected with the control device 27 as well, so that an indirect connection between detector 26 and control device 27 is established). The control device is thus informed about the presence or absence of the marking 21 (or 20 on other blanks) on each blank. A further detector 26′ may be present below the transport plane for the blanks detecting markings provided on the underside of the blanks. A signal line 31′ connects this detector to the control device 27 as well. Accordingly, the control 27 knows whether the rounded blank that has been rounded from blank 18 and will be entering the welding rollers 23, 23′ after a known number of preceding rounded blanks 28, 29 is a rounded blank with a tin coating of greater thickness than the normal tin coating in the longitudinal weld seam area or not. The control 27 can then set welding parameters to match the thicker coating if such a coating has been detected by the presence of a marking. The parameter(s) that can be influenced by the control is one parameter or are several of the parameters of the group of amount of electric welding current (in Ampere), shape of the electric welding current (sinus shape, rectangular shape, triangular shape or other shapes as provided by the welding current generator of the welding apparatus) and/or welding current frequency. It is as well within the scope of the invention to additionally or alternatively to the welding current control to control or change, respectively, the welding force by changing the pressure with which the welding rollers act on the body to be welded, dependent on the presence or absence of the marking 20, 21. For body blanks with variant I cuts of FIG. 4 the welding parameter(s) selected is/are kept at the selected value for the whole length of the weld seam of this body blank. For body blanks with variant II cuts of FIG. 4 the single or the several parameters for thicker coating are only active for the begin or the end of the weld seam. In this case the marking will indicate by different markings whether the welding parameters have to be adapted for the beginning of the weld seam or for the end of the weld seam.

Detectors 26, 26′ can be present on any location of can body making apparatus 35 where the detection of markings 20, 21 before welding of the blank with these markings is possible. A preferred location is the shown placement in front of the rounding apparatus 24.

The marking(s) may contain only the information whether there is a coating of elevated thickness or not. If not, the normal coating thickness range is present on the blank. On the other hand the marking provides the possibility to give more information about the coating and in particular to consider by the marking the result of a coating thickness measurement (which can be made by any of the thickness measurement methods known to the skilled person). Thus the marking will give an indication not only that there is an elevated coating thickness present on a specific blank but will indicate at least in which of two different ranges of elevated coating thickness the coating of the present blank falls. This can then trigger a different selection of welding parameters depending on the range of elevated coating thickness. For such an embodiment the marking device applying the marking to the blank must be able to receive and to consider information from the thickness measuring device for adapting the actual marking accordingly, by making different markings for different tin range blanks. In FIG. 4 a thickness measurement is schematically indicated by arrow A and the marking responsive to this measurement by arrow B. The thickness measurement can as well be provided in the slitter of FIG. 1 and then the marking in the slitter will as well be indicative of the thickness.

For the case of a marking without thickness measurement the marking device has only to deliver (continuously or discontinuously) a single marking by delivering the marking substance to the blank. The marking can be done by different kind of colours and can be visible to the human eye or not. The marking can be done by substances that can only be detected in the ultraviolet light range or by magnetic lacquers or other magnetic substances. The detection devices 26, 26′ have to be adapted accordingly to detect the used marking substance and thus the marking. Such devices are known to the skilled person.

In the description it has been explained that the sheet metal blanks with greater thickness coating are marked. This is the preferred embodiment. But in an alternative embodiment a mark could instead be applied only to the sheet metal blanks having the uniform thickness coating so that the blanks with higher thickness coating remain without such a mark and the other blanks carry the mark. In this case the claimed marking lies in the absence of a mark indicating uniform thickness. This allows as well making the difference in the welding step for the container body blanks between blanks with a higher thickness coating and blanks with the normal coating. The welding parameters are in this case adapted for the blanks without a mark.

Thus a method for marking tin coated sheet metal blanks is provided in which the marking is indicative whether the blank comprises an edge region that includes a thicker tin coating than the rest of the blank. This marking is preferably brought on the blanks when a plurality of blanks is cut from a sheet metal plate. In the alternative the marking may have been applied to the sheet metal plate already. The sheet metal blanks thus marked are provided in form of a stack comprising marked and unmarked blanks, depending on whether there is a thicker edge region coating present on the individual blank or not. When making container bodies of these blanks by de-stacking and rounding the sheet metal blanks and welding the longitudinal seam of the rounded container body blanks, the marking is read in the container making apparatus and at least one welding parameter is changed for welding container body blanks with a marking in comparison with container body blanks without marking.

While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practised within the scope of the following claims. 

1. A method for providing sheet metal blanks with a coating on one side or on both sides thereof, comprising the steps of: cutting a plurality of blanks from a one-sided or double-sided coated sheet metal plate that has two opposite edge regions of the sheet metal plate with a greater coating thickness than in the region between the edge regions, the cutting providing sheet metal blanks including such edge regions of the plate and sheet metal blanks devoid of such edge regions of the plate, applying a machine-readable marking to the sheet metal that indicates the regions of greater thickness, and collecting the cut sheet metal blanks to form a stack which includes blanks with such marking and blanks without such marking.
 2. A method according to claim 1 wherein the coating is a tin coating.
 3. A method according to claim 1 wherein the stack is collected from blanks cut from several sheet metal plates.
 4. A method according to claim 1 wherein the marking is applied during the step of providing the sheet metal plates by cutting such plates from a sheet metal band.
 5. A method according to claim 1 wherein the marking is applied to the sheet metal during the step of coiling a sheet metal band to form a coil or during the step of uncoiling a sheet metal band from a coil and wherein the sheet metal plates are provided by cutting sections from the sheet metal band.
 6. A method according to claim 1 wherein the marking is applied in a double slitter in which the metal plates are cut by cutters arranged at a right angle to each other to form the plurality of blanks from each sheet metal plate.
 7. A method according to claim 1 wherein the marking is provided by a marking substance invisible to the human eye.
 8. A method according to claim 1 including the steps of performing coating thickness measurements in the regions of coating with greater coating thickness and applying different markings dependent on the measurement results providing the sheet metal blanks with different markings indicative of different thickness values.
 9. A stack of tin coated sheet metal blanks of the same size provided for making container body blanks contains sheet metal blanks including an edge region of the blank with a tin coating thicker than outside of the edge region of said blank, and wherein the stack contains sheet metal blanks without a tin coating in the edge region of the blank thicker than outside of the edge region of said blank and wherein the blanks with the thicker edge region coating are provided with a machine readable marking indicative of the thicker coating.
 10. A method for making container bodies from single sheet metal blanks made by the method of claim 1 and provided on a stack according to claim 9, comprising the steps of consecutively de-stacking sheet metal blanks, rounding the sheet metal blanks, providing a succession of rounded container body blanks, and feeding the container body blanks in a welding apparatus for welding the longitudinal seam of the body blanks by welding rollers and wire electrodes and with welding parameters controlled by a control device, wherein marking provided on said sheet metal blanks is machine-read and at least one of said welding parameters is controlled for each consecutive blank dependent on the machine-reading of the marking.
 11. A method according to claim 10 wherein the parameter is selected from the group of welding force, amount of welding current, welding current shape, welding current frequency.
 12. A method according to claim 10 wherein the markings are machine-read before rounding of the sheet metal blanks.
 13. A double slitter for cutting sheet metal plates into a plurality of sheet metal blanks of the same size, comprising a stack receiving section for taking up a stack of sheet metal plate, a first cutting device for cutting the sheet metal plates into a first number of sheet metal strips and a second cutting device arranged at a right angle to the first cutting device for cutting the sheet metal strips into a second number of sheet metal blanks, wherein the double slitter comprises at least one marking device for applying a machine readable marking onto two opposing edge regions of the sheet metal plate before or during cutting thereof or on cut strips or blanks.
 14. A double slitter according to claim 13 wherein the marking devices are arranged on both sides of the stack receiving section.
 15. A container body making apparatus comprising a receiving section for receiving a stack of metal sheet blanks, a de-stacker for de-stacking from the stack, a rounding apparatus arranged for taking up the de-stacked blanks and outputting rounded container body blanks and a welding machine for welding the longitudinal seam of the container body blanks fed from the rounding apparatus to the welding machine, said welding machine comprising an upper and a lower welding roller and wire electrodes running on the welding rollers and a welding current generator controlled by a controller, wherein the container body making apparatus comprises at least one detection device for detecting the presence of machine-readable markings being present or not being present on consecutive sheet metal blanks and on a predefined area on the sheet metal blanks, and wherein the at least one detection device is connected to said controller, the controller being adapted to control the welding current generator dependent on a signal from the detection device.
 16. A container body making apparatus according to claim 15 wherein the controller is arranged to control the welding force applied by the welding rollers dependent on the signal from the detection device.
 17. A method according to claim 2 wherein the stack is collected from blanks cut from several sheet metal plates.
 18. A method according to claim 11 wherein the markings are machine-read before rounding of the sheet metal blanks. 